Still, if you're a hot, sweaty mess 10 minutes into your workout, it doesn't necessarily mean you're not fit. Different people have different numbers of sweat glands, so even a brisk walk to the mailbox can trigger sweat production in some women.

On the flip side, if you're working hard and hardly sweating, you might be super-fit, blessed with minimal sweat glands, or dehydrated. After all, sweating depends on having water to spare.

To keep your tank full, Scott recommends downing about 24 ounces of water (that's about how much most sports bottles fit) before your warm-up, and drinking about 8 more every 30 minutes throughout your sweat sesh. Keep sipping throughout the day, and keep in mind that if you feel thirsty, you're probably already dehydrated.